1. Field of the Invention
The present invention relates to a roller bearing for endless linear motion in which a casing mounted on a track rail of linear shape can make an endless linear motion through a plurality of rollers circulating endlessly. It is a bearing in which cylindrically shaped rollers are used as rolling bodies which bear loads of all directions such as upward, downward, forward, rearward, rightward or leftward, as the bearing makes an endless linear motion. Moreover, the present invention aims to provide the most compact roller bearing for linear motion from the viewpoint of sectional height and width of the bearing in comparison with prior art bearing for the same load capacity.
2. Description of the Prior Art
In the prior art roller bearing for endless linear motion, for instance, as shown in FIG. 3, although casing 4 mounted on track rail 6 can make endless linear motion through a plurality of roller 7, the position of return hole, which circulates roller 7 rolling in load track 2 through direction changing path, is such that the center of the return hole lies on the bisecting plane of the right angle V groove 3 of load track 2, as shown by 1a . If the return hole 1a is provided at this position, the return hole will be in a position close to a preload bolt of the preload device which preloads bearing plate 20 (FIG. 3) provided with right angle groove 3, according to the condition of use of the bearing. In such case, the preload device can be placed only at a position out of a circulating path consisting of load track 2, return hole 1a, and the direction changing paths at both ends, namely, only at two places, or, at front and rear ends in the direction of the linear motion and a wedge device may be used in combination. As a result, proper preload cannot be imposed throughout the length of the load track causing insufficient functioning of the preload device. Thus not only the width of the casing 4 is increased but the length is increased for an amount necessary to install the preload device, and the compactness of the bearing is prevented.
Also, FIGS. 24 and 25 show an arrangement of U.S. patent application Ser. No. 499,367 filed on May 31, 1983 by the present applicant. In this arrangement, the direction change of rollers 42 is made from load track 43 to upwardly inclined return hole 44 through direction changing path 48 that is formed in a circular arc shape both for its horizontal and vertical projections. In comparison with prior art, this arrangement allowed a plurality of preload bolts 47 to be provided at positions approximately close to the bisecting plane of right angle V groove 45 of load track 43 and at positions close to return hole 44. Thus, it was possible to achieve a compact bearing. However, since the return hole 44 is provided at A portion shown in FIG. 3, there is a tendency to decrease the strength near A portion of casing 4. For this reason, it is necessary to increase the width b of a depending portion 5 of the casing 4 (shown in FIG. 3) where the preload device is installed. Also the height of the casing which is mounted on track rail 40 has to be increased for an amount corresponding to the upwardly inclined return hole. Thus, although compactness was induced in comparison with the prior art described previously, there was still a limitation in compactness. The spacially curved shape of the direction changing path was also complicated, and thus the processing of the direction changing path was difficult.
Further, in case a roller bearing for linear motion is used on machine tools, etc., ball threads, fluid cylinders, etc. for driving purpose are often installed in-between load tracks at both sides. In such cases, it is desired that inner width B.sub.1 of the casing shown in FIGS. 1 and 26 be made large. But the width of the bearing affects the overall width of the apparatus, and if the outer width B.sub.2 of the casing shown in FIGS. 1 and 26 is increased, the required installation area of the bearing will become large, and thus there was a strong demand that the width (B.sub.2 -B.sub.1)/2, which is a depending portion of the casing, be made as small as possible.